This invention relates to a process for preparing a rigid, hydrocarbon blown, polyurethane foam by reacting a polyisocyanate with a polyol composition comprising a fatty oil, notably castor oil.
A recent trend in the manufacture of polyurethane foam, especially rigid polyurethane foam, is the use of hydrocarbon blowing agents as substitute or replacement for the traditionally employed blowing agents including trichlorofluoromethane. Such trend has been motivated by the desire to eliminate the use of certain fully halogenated alkanes in an effort to protect the environment including the ozone content of the atmosphere. The general use of hydrocarbons as a blowing agent for polyurethane foam is widely reported in the literature. For example, U.S. Pat. No. 5,096,933 discloses the use of cyclopentane, cyclohexane or mixtures thereof. U.S. Pat. No. 5,182,309 discloses the use of pentane. U.S. Pat. No. 5,001,164 discloses the use of pentane in combination with trichloroethane. U.S. Pat. No. 5,286,759 discloses combinations of hydrocarbons containing at least 4 carbon atoms with perfluoroalkanes as a blowing agent for polyurethane foam manufacture. U.S. Pat. No. 4,263,412 discloses the preparation of polyurethane foam in the presence of butane. Of the mentioned hydrocarbons, use of cyclopentane and pentane is presently favored due to availability and general benefit to the physical properties of the foam.
However, to prepare polyurethane foam which exhibits attractive physical properties, advantageously all reactants should be readily miscible with one and another and/or high efficiency mixing procedures be employed to ensure even distribution of all starting materials. In the presence of poor miscibility or poor mixing, the resulting foam may exhibit inferior, unattractive, physical properties. Hydrocarbon blowing agents, especially when used in significant amounts as might be required to produce a low density foam, are generally not noted for having attractive miscibility with the majority of polyester or polyether polyols commonly used to prepare polyurethane foam. Frequently separation results leading to poor mixing and/or poor foam quality.
In the art when problems of miscibility are encountered, using the traditional type of blowing agents, frequently they can be resolved by varying the amount of cell stabilizing agent or surfactant present in the foaming process. In many instances, the problem has been resolved by use of a surfactant in an amount of from about 0.1 to about 2 parts per 100 parts of polyol. Use of greater amounts of surfactants, normally a mineral oil of the polysiloxane type, can lead to a significant decline in the physical properties of the resulting foam. For closed-cell rigid polyurethane foam, this can be a reduction of compressive strength, a loss of thermal insulation potential as a consequence of an acquired open-cell content, or poor mold filling (flow) characteristics. When preparing low density polyurethane foam in the presence of a hydrocarbon blowing agent with elevated loadings of the conventional surfactants, the poor miscibility problem is not satisfactorily resolved. Accordingly it would be desirable to provide for an alternative foaming process permitting the manufacture of polyurethane foam, especially low density foam, in the presence of a hydrocarbon blowing agent which does not suffer from the above mentioned deficiencies.
For this purpose, the use of hydroxyl-containing fatty oils has been investigated.